The application of co2 laser for printed circuit board

1. The Application of CO2 Laser for
Printed Circuit Board (PCB)
Guided Reading: Two laser techniques can be used in laser drilling
processing. CO2 laser wavelength is within far ultrared-ray waveband and
ultraviolet laser wavelength is within UV band.
Recource: wikipedia
It has high productivity in large-size hole manufacturing, because it
needs CO2 laser wavelength is within far ultrared-ray waveband and
ultraviolet laser wavelength is within UV band. CO2 laser is widely used
in micro-vias production of printed circuit board, requiring micro-vias'
diameter greater than 100μm(Raman, 2001). It has high productivity in
large-size hole manufacturing since it needs very short time to finish
punching by CO2 laser. UV laser technology is widely applied in micro-vias
production, with diameter less than 100μm even 50μm. It has high output
when produce holes with diameter less than 80μm. Therefore, more and more
manufacturers have brought in double-ended laser hole-drilling system in
order to meet the increasing demand of micro-vias production. Below are
the three main types of double-ended laser hole-drilling system in current
market:
1) double-ended UV drilling system;
2) double-ended CO2 laser drilling system;
3) mixed laser drilling system (with both CO2 and UV).
Each type has its merit and demerit. Laser drilling system includes
double-ended single wavelength system and double-ended dual-wavelength
system. Two parts influence the drilling quality:
1) laser power / pulse energy;

2. 2) beam positioning system.
Laser pulse energy and transmission efficiency of beam decide the drilling
time, which means the period of time needed to drill a micro-via by laser
drilling machine. Beam positioning system decides the speed of movement
between two holes. The speed of laser drilling machine is determined by
all the factors together. Double-ended UV drilling system is ideally
suited to drilling less than 90μm in integrated circuit, with high aspect
ratio.
Double-ended CO2 laser drilling system makes use of Q-switch RF-excited
CO2 laser. It's principle advantages include high repetition rate (which
reaches to 100kHz), short drilling time and wide interface.
Mixed laser drilling system is the most popular system composed of UV laser
head and CO2 laser head. The comprehensive application of mixed laser
drilling methods allows both copper and dielectric medium drilling occur
at the same time. Ultraviolet radiation drill the copper to form a
particular size and shape, and CO2 laser drill the uncovered dielectric
adjacently. The drilling process is to drill a 2inX2in area, which is
called domain.
Recource : bnl.gov
CO2 laser can remove dielectric effectively, even the non-uniform
glass-reinforced dielectric. However, it is unable to drill hole less than
75μm and remove copper, with an exception of pre-treated thin copper foil

3. (lustino, 2002) less than 5μm. UV laser can drill very small holes and
erase every ordinary copper (3-36μm，1oz，even electro copper foil). It
can also erase dielectric material by itself but it is quite slow. And
the result is not good on non-uniform materials like glass-reinforced FR-4.
It is because that only when the energy density is improved to some extent,
the glass can be successfully removed but bonding pad will be destroyed
in the meantime. Since mixed laser drilling system contains both CO2 and
UV laser, it can achieve the best result in the two fields, with UV laser
in copper foil and small hole and with CO2 laser in fast drilling on
dielectric.
At present, the distance between the two heads is fixed in most
double-ended laser hole-drilling system, with stepping-repeat beam
positioning technology.
Stepping-repeat laser remote controller has large regulating range,
reaching to 50X50 μm. Its disadvantage is that the laser remote
controller has to move in the fixed area, and the separation distance
between the two heads is fixed as well. Typical separation distance
between the two heads is about 150μm. It is impossible to get the optimum
allocation operation like programmable head when it comes to different
panel sizes.
Nowadays, there are various specification of performance for double-ended
laser hole-drilling system, which can apply to small printed circuit board
(PCB) manufacture as well as mass production.

4. Ceramic aluminum oxide is used in printed circuit board (PCB) manufacture
for its high dielectric constant. But it is frangible and the mechanical
pressure in drilling need to reduce to the minimum, which is an advantage
for laser drilling. Rangel had proved in 1997 that Q-switch Nd - YAG laser
drilling can be applied in aluminum oxide baseboard and aluminum oxide
baseboard covered with gold and anchor. Laser with short pulse, low energy
and high-peak power can protect sample from mechanical pressure and make
high quality hole less than 100μm.